Electrochemical sensors such as biosensors have been used for many years. Among other applications, they now play an important role in the daily monitoring of blood glucose levels in diabetic patients, who sometimes perform four or more measurements per day. Once the glucose level is determined, action regarding adjustment of the insulin or glucose level in the blood is initiated. Serious and life-threatening consequences can result if the patient's blood glucose falls too low or becomes too high. Beyond the benefits of alerting a patient to the extremes, controlling blood glucose levels is considered to reduce incidence reduction of kidney, nerve, and retinal damage that can otherwise result from poor control. Clearly, the accuracy of the electrochemical measurements is critical to the health and well-being of the patient.
Known electrochemical sensors typically comprise a planar substrate, a working electrode and a counter or reference electrode on the substrate, a reagent comprising an enzyme and mediator on the working electrode, and a means for transporting the fluid sample to the electrode surface. The electrodes are arranged so that a signal representing the analyte concentration can be generated. The measurement technique is typically amperometric where a known voltage is applied and current is generated by the biochemical reaction (e.g., glucose reaction) and measured by an electronic device (meter). These reactions usually include an initial reaction with the enzyme that is selective for an analyte (e.g., glucose) in a sample, and a mediator that shuttles electrons between the enzyme and a working electrode. In this case, the sensor includes at least one counter or reference electrode and one working electrode. The reactant layer also can include other components that participate in the reaction or perform other functions. Other measurement techniques mentioned in the literature are coulometric and voltametric methods.